The present invention relates generally to turbomachinery, and more particularly, to an assembly for attaching blades to an associated rotor of the turbomachine.
Generally, a turbomachine will include series of blades attached to a rotor which is axially disposed within an outer casing. To retain the blades to the rotor, the base of each blade is provided with a dovetail portion and the rotor is provided with a series of slots which are correspondingly configured to the dovetail portion of the blades. In assembly, the dovetail portion of the blade is located within a slot of the rotor, and the assembly is appropriately secured in position, for example, using a retaining ring.
To facilitate assembly of the unit, as well as subsequent repairs, a clearance is provided between the dovetails of the blades and the slots of the rotor. Although helpful during assembly and servicing of the turbomachine, such tolerances tend to permit relative motion between the blades and rotor when assembled. In many cases, this motion may be maintained to an acceptable level. However, particular difficulty in this regard has been encountered in connection with the blades associated with the fan portion of the turbomachine, since these blades are traditionally significantly longer than the blades associated with the remaining portions of the turbomachine.
Problems associated with fan blade motion have long been recognized, and steps have been taken to ameliorate these problems. For example, fan blades are often provided with cooperating surfaces or protrusions which combine and cooperate to develop what are known as "interlocking blade shrouds". Properly configuring the series of protruding surfaces associated with the blades has been found to limit blade motion or rotation resulting from clearances between the dovetail of the blade and the slot which engages it.
Although reducing unwanted blade motion in many cases, particular difficultly has been found in connection with movement resulting from ambient wind conditions and the effects of such conditions upon a non-operating turbomachine. Such ambient wind conditions, passing through the various portions of the turbomachine and encountering the associated series of blades, tend to produce an effect known as "wind-milling", resulting in movement of the rotor within the turbomachine. In connection with this wind-milling effect, a phenomenon known as "clanking" often occurs, wherein the blades rotate within the slots of the rotor during wind-milling. Again, in view of their length, this phenomenon is particularly prevalent in connection with fan blades. Such blade motion can eventually lead to premature wear and subsequent failure along various portions of the blade, particularly along the blade dovetail and the protrusions which combine to develop the interlocking blade shroud, as well as in connection with the structure which is used to retain the blades to the rotor.
Recognizing this problem, workers skilled in the art have attempted to overcome the problems associated with clanking in an effort to reduce fatigue and possible failure of blade components. Examples of this may be found, for example, in U.S. Pat. Nos. 3,930,751 and 3,572,970. However, neither of these solutions have been found to be entirely satisfactory and it therefore remains to develop an anti-clanking assembly which is effective in overcoming the foregoing disadvantages.